Integrated Assessment of Selectivity, Soil Behavior, and Biochar-Mediated Release for the Botanical Herbicide Precursor S-(-)- Spirobrassinin

Abstract

S-(-)-Spirobrassinin is a secondary metabolite derived from broccoli, exhibiting significant weed-suppressive activity and serving as a promising lead compound for botanical herbicide development. However, its practical application is constrained by unanswered questions regarding crop selectivity, environmental fate, and particularly its rapid soil degradation. To address these gaps, this study employed a combination of bioassays, soil analytics, and molecular dynamics simulations to comprehensively evaluate its herbicide potential and explore a biochar-based carrier strategy for sustained release. Our results demonstrated that S-(-)-Spirobrassinin exhibited differential tolerance on Setaria italica compared to Sorghum bicolor, Avena sativa and Brassica napus, while demonstrating superior efficacy against graminaceous weeds over broadleaf weeds, indicating a notable degree of selectivity. Soil incubation experiments revealed that the compound degraded rapidly, with only 2.7 μg/mL detectable after 21 days, and induced transient shifts in microbial community structure, reducing overall diversity and altering the relative abundance of key phyla such as Proteobacteria and Actinobacteria. To overcome the degradation limitation, molecular simulations revealed that S-(-)-Spirobrassinin can be strongly adsorbed onto carbonaceous surfaces and confined within micropores, underpinning the theoretical basis for using biochar as an effective controlled-release carrier. This work not only elucidates the crop selectivity and soil behavior of S-(-)- Spirobrassinin but also proposes a mechanism informed strategy to enhance its persistence, providing a holistic foundation for developing this natural product into an eco-friendly smart herbicide system.